US6901177B2 - Optical top hat pulse generator - Google Patents

Optical top hat pulse generator Download PDF

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US6901177B2
US6901177B2 US10/341,689 US34168903A US6901177B2 US 6901177 B2 US6901177 B2 US 6901177B2 US 34168903 A US34168903 A US 34168903A US 6901177 B2 US6901177 B2 US 6901177B2
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optical
signal
top hat
coupler
pulses
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Stanislav I. Ionov
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HRL Laboratories LLC
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/508—Pulse generation, e.g. generation of solitons
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/3515—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam
    • G02F1/3517—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam using an interferometer
    • G02F1/3519—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam using an interferometer of Sagnac type, i.e. nonlinear optical loop mirror [NOLM]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters

Definitions

  • the present invention relates to coherent detection of pulse position modulated signals. More particularly, the present invention relates to a top hat optical pulse generator for use within a pulse position modulation receiver.
  • PPM Pulse Position Modulation
  • PPM signals are usually demodulated from the optical to electronic domain by a photodiode followed by a lowpass filter (LPF) that converts pulse position modulation to amplitude modulation.
  • LPF lowpass filter
  • Such a demodulation technique is not capable of recovering the DC component, since the DC component is represented by a constant temporal shift of all pulses from their unmodulated positions.
  • the demodulated signals after the lowpass filter have very low amplitude at low frequencies. The amplitude increases linearly with frequency up to the Nyquist limit. Such frequency-dependent distortion is corrected by an integration circuit, which amplifies low-frequency noise accordingly, resulting in decreased SNR performance.
  • An advantage of embodiments of the present invention is to provide an apparatus and method for generating optical pulses with a top hat shape.
  • An additional advantage of embodiments of the present invention is to provide a method and apparatus for the detection of pulse position modulated optical signals using optical top hat pulse generators.
  • An optical top hat pulse generator comprises a non-linear optical loop mirror (NOLM) that is fed by a continuous wave (CW) optical signal and is controlled by incoming optical pulses comprising first order solitons.
  • NOLM non-linear optical loop mirror
  • CW continuous wave
  • the soliton regime for the incoming optical pulses is obtained by choosing a fiber with the correct dispersion and by adjusting the peak power of the control pulses.
  • the use of soliton control helps assure no spread of the control pulse, since the shape of the control pulse is maintained by fiber nonlinearity.
  • a first embodiment of the present invention provides a top hat pulse generator receiving a continuous wave optical signal at a first wavelength and a pulsed optical signal at a second wavelength and generating top hat optical pulses at the first wavelength
  • the top hat pulse generator comprising: an optical coupler having a first side with a first arm and a second arm and a second side having a third arm and a fourth arm, the first arm adapted to receive the continuous wave optical signal and to launch the continuous wave optical signal into the third arm and the fourth arm; an optical fiber having a first end and a second end, the first end disposed to receive optical energy from the third arm and to transmit optical energy to the third arm and the second end disposed to receive optical energy from the fourth arm and to transmit optical energy to the fourth arm, the optical fiber having a positive dispersion supporting optical solitons; an optical filter receiving optical energy from the second arm; and a control pulse coupler positioned to launch optical energy into the optical fiber, the control pulse coupler having an input adapted to receive the pulsed optical signal, wherein the
  • Another embodiment of the present invention provides a method for converting optical pulses at a first optical wavelength to top hat optical pulses at a second optical wavelength comprising the steps of: generating a continuous wave optical signal at the second optical wavelength; launching counter-propagating beams of the continuous wave optical signal into a loop of optical fiber from a coupler, the optical fiber having a positive dispersion supporting optical solitons and the counter-propagating waves interfering at the coupler; launching the optical pulses into the loop of optical fiber, the optical pulses having a peak optical power; controlling the peak optical power to a power of a first order soliton; coupling optical energy out of said optical fiber at said coupler; and filtering the optical energy to suppress optical energy at the first optical wavelength and to pass optical energy at the second optical wavelength to produce top hat optical pulses at the second optical wavelength.
  • Still another embodiment of the present invention provides an apparatus for detecting a pulse position modulated optical signal comprising: a clock source providing a pulsed optical clock signal synchronized to the pulse position modulated optical signal; a continuous wave optical source producing a continuous wave optical signal; a first optical top hat pulse generator receiving the continuous wave optical signal and the pulse position modulated signal and producing a first optical top hat output signal, wherein a peak power of the pulse position modulated signal is adjusted to that of a first order soliton; a second optical top hat pulse generator receiving the continuous wave signal and the pulsed optical clock signal and producing a second optical top hat output signal, wherein a peak power of the pulsed optical clock signal is adjusted to that of a first order soliton; and an overlap-to-electric converter receiving the first optical top hat signal and the second optical top hat signal and producing an electric signal proportional to an overlap amount between the first optical top hat signal and the second optical top hat signal.
  • Yet another embodiment of the present invention provides a method for detecting a pulse position modulated signal comprising the steps of: receiving the pulse position modulated optical signal; providing a stream of optical clock pulses; generating a continuous wave optical signal having an optical wavelength different than an optical wavelength of the pulse position modulated signal or the optical clock pulses; applying the continuous wave optical signal to a first non-linear optical loop mirror; coupling the pulse position modulated optical signal into said first non-linear optical loop mirror; controlling a peak power of the pulse position modulated optical signal to be at a power of a first order soliton; applying the continuous wave optical signal to a second non-linear optical loop mirror; coupling the stream of optical clock pulses into the second non-linear optical loop mirror; controlling a peak power of the stream of optical clock pulses to be at a power of a first order soliton; coupling a first output optical signal out of the first non-linear optical loop mirror; filtering the first output optical signal with a filter that transmits around the optical wavelength of said continuous wave optical signal and
  • FIG. 1 shows a block diagram of an optical pulse position modulation receiver in accordance with the present invention.
  • FIG. 2 shows a block diagram of an optical pulse position modulation receiver using correlation of top hat pulses to provide an electrical output.
  • FIG. 3 shows a schematic representation of a typical non-linear optical loop mirror.
  • FIG. 4A shows a schematic diagram of an optical correlator for use in the receiver depicted in FIG. 2 .
  • FIG. 4B depicts a sum frequency generation apparatus for performing overlap to electric conversion.
  • FIG. 4C depicts a four-wave mixing apparatus for performing overlap to electric conversion.
  • FIG. 5 shows a graphical view of the transformation of the optical pulses to a current output by the top hat pulse generators and correlator depicted in FIG. 2 .
  • FIG. 6 shows a block diagram of an embodiment of a top hat generator controlled by first order solitons according to an embodiment of the present invention.
  • FIG. 7 is a graph of the conversion efficiency versus relative de-tuning of an embodiment of a top hat generator according to the present invention where the duty cycle of the output pulses is assumed to be 0.45.
  • FIG. 8 is a graph of the relative cross-talk versus relative de-tuning of an embodiment of a top hat generator according to the present invention.
  • FIG. 1 depicts an optical receiver 50 that detects optical pulse position modulated signals and converts the detected pulses to an electrical waveform.
  • the optical receiver receives both short optical clock pulses 11 and short pulse position modulated optical pulses 21 .
  • the short optical clock pulses 11 which have a fixed period, are converted to rectangular clock pulses 13 by, preferably, a first top hat generator 10 .
  • the short optical signal pulses 21 which vary in temporal position according to the modulated optical signal, are converted to rectangular signal pulses 23 by, preferably, a second top hat generator 20 .
  • An overlap-to-electric converter 30 detects the amount of overlap 33 between the rectangular clock pulses 13 and the rectangular signal pulses 23 and converts the overlap amount 33 into an electrical signal.
  • the overlap amount is a measure of the delay between the optical clock pulses 11 and the pulse position modulated signal pulses 21 .
  • the overlap-to-electric converter 30 may comprise a coherent correlator, a sum frequency generator, a four-wave mixer, or other means that can measure the amount of overlap between separate streams of rectangular pulses and output the measured amount as an electrical signal.
  • overlap to electric conversion may be achieved by any of several methods known in the art.
  • an exemplary coherent correlator 140 is shown in FIG. 4 A and described in additional detail below, in relation to the circuit depicted in FIG. 2 .
  • the overlap-to-electric converter 30 may also comprise a sum frequency generator or a four-wave mixer. Sum frequency generators are well-known in the art.
  • An exemplary sum frequency generator is depicted in FIG. 4 B and described in additional detail below.
  • An exemplary four-wave mixing apparatus is depicted in FIG. 4 C and described in additional detail below.
  • additional methods and apparatus may be used to provide overlap to electric conversion. The description of the specific apparatus and methods herein should not be construed to limit embodiments of the present invention to these apparatus and methods.
  • FIG. 2 depicts an embodiment of the optical receiver 100 described in U.S. Pat. No. 6,462,860.
  • a first top hat generator 110 receives a pulse position modulated optical signal P sig ( ⁇ sig ) and a continuous wave optical signal CW( ⁇ CW ), and produces a rectangular signal pulse output RP sig ( ⁇ CW ). Still referring to FIG.
  • a second top hat generator 120 receives a pulsed optical clock signal P clk ( ⁇ CW ) and the continuous wave optical signal CW( ⁇ CW ), and produces a rectangular clock pulse output RP clk ( ⁇ CW ).
  • a continuous wave source 130 provides the continuous wave optical signal CW( ⁇ CW ).
  • An optical pulse source (not shown) provides the pulsed optical clock signal P clk ( ⁇ clk ) such that the optical pulses in the pulsed optical clock signal P clk ( ⁇ clk ) are preferably equally spaced or nearly equally spaced in time.
  • Optical pulse sources providing pulsed optical signals are known in the art.
  • the PPM optical signal P sig ( ⁇ sig ) and the pulsed optical clock signal P clk ( ⁇ clk ) may have the same or different optical wavelengths.
  • the rectangular signal pulse output RP sig ( ⁇ CW ) and the rectangular clock pulse output RP clk ( ⁇ CW ) are synchronized and are coherent since both derive their optical frequency and phase from that of a single continuous-wave source.
  • a coherent correlator 140 receives the rectangular signal pulse output RP sig ( ⁇ CW ) and the rectangular clock pulse output RP clk ( ⁇ CW ) and produces a current output I s (t).
  • the output I s (t) of the coherent correlator 140 is proportional to the cross-correlation product of the rectangular signal pulse output RP sig ( ⁇ CW ) and the rectangular clock pulse output RP clk ( ⁇ CW ). This cross-correlation product is also proportional to the offset in time between each PPM pulse and its corresponding clock pulse.
  • the output of the coherent correlator 140 provides a demodulated analog signal corresponding to the original analog pulse position modulated signal.
  • the top hat generators 110 , 120 of the present invention each preferably comprise a nonlinear optical loop mirror (NOLM) with a control loop.
  • NOLMs are well known in the art and can be constructed by splicing together commercial fibers and couplers.
  • U.S. Pat. No. 5,208,455 issued to B. P. Nelson et al. on May 4, 1993, describes the construction of a typical nonlinear optical loop mirror.
  • Non-linear optical loop mirrors are also further described by S. Bigo, O. Leclerc, and E. Desurvire in “All Optical Fiber Signal Processing and Regeneration for Soliton Communications,” IEEE J. Sel. Topics Quant. Electron., Vol. 3 (1997), p 1208.
  • FIG. 3 depicts a typical NOLM 500 .
  • the NOLM 500 comprises a first coupler 510 for coupling a continuous wave optical signal OPT CW into the NOLM 500 and a second coupler 520 for coupling an optical control pulse OPT CP into the NOLM 500 .
  • the optical loop of the NOLM is formed by an optical fiber 550 that is routed from one branch of the first coupler 510 to another branch of the first coupler 510 .
  • a filter 560 may be disposed at another branch of the first coupler 510 to filter out signals at the optical wavelength of the optical control pulse, while allowing signals at the optical wavelength of the continuous wave optical signal to pass from the NOLM 500 .
  • the single frequency continuous wave source 130 operating at an optical wavelength ⁇ cw feeds into the top hat generators 110 , 120 comprising NOLMs.
  • Both NOLMs are preferably completely symmetrical so that the continuous wave radiation is reflected completely in the absence of control radiation.
  • the signal and clock pulses at wavelengths ⁇ sig and ⁇ clk act as control signals in the NOLMs.
  • the wavelengths of the control signals ⁇ sig and ⁇ clk must be different than that of the continuous wave radiation at ⁇ cw .
  • the NOLMs preferably provide pulses with top hat temporal shapes.
  • the coherent trains of rectangular signal RP sig ( ⁇ CW ) and clock pulses RP clk ( ⁇ CW ) at the continuous wave frequency ⁇ cw are combined in the optical correlator 140 .
  • the optical correlator 140 consists of a 3 dB coupler 141 and a balanced detector 143 , as shown in FIG. 4 A.
  • an optical correlator is one way to provide the overlap-to-electric converter used in embodiments of the present invention.
  • a sum frequency generation apparatus 440 may also be used. Such circuits are well-known in the art.
  • the sum frequency apparatus 440 comprises a lens 441 for focusing beams comprising the top hat pulses of the clock TH clk 446 and the signal TH sig 447 into a non-linear crystal 443 .
  • the non-linear crystal may comprise lithium niobate.
  • the two beams 446 , 447 are directed through the non-linear crystal 443 , where they produce sum-frequency beam 448 , which propagates within the sector between the two beams 446 , 447 to an aperture 445 .
  • the sum-frequency radiation is generated only when the clock pulses and the signal pulses overlap in time. Therefore, the electric current from the photodetector 449 is proportional to the amount of overlap.
  • FIG. 4C depicts a four-wave mixing apparatus well known in the art.
  • the top hat pulses of the clock TH clk at a wavelength ⁇ clk and the signal TH sig at a wavelength ⁇ sig are directed into a single mode fiber 450 , which is preferably dispersion shifted fiber.
  • the length of the fiber should be below the fiber dispersion length for the top hat pulses.
  • a photodetector may then be used to detect and convert the four-wave output signal to an electric signal that is proportional to the overlap between the clock and signal pulses.
  • FIG. 5 show the relationship between the input optical clock pulses 11 and the pulse position modulated signal pulses 2 land the correlator current 74 produced by the optical correlator 140 depicted in FIG. 2 .
  • the greater the overlap 33 between the rectangular clock pulses 13 and the rectangular signal pulses 23 the greater the correlator current 74 produced by the optical correlator 140 .
  • devices other than an optical correlator may be used to detect the overlap 33 and to output an electrical signal based on the overlap.
  • the linearity of an optical PPM receiver using top hat generators depends on the quality of the rectangular pulses generated by the top hat generators.
  • the quality of the rectangular pulses is essentially the closeness of the shape of the generated pulses to a true “top hat” shape.
  • the control pulse which imprints a non-linear phase shift on the co-propagating CW beam as described above, preferably retains its shape along the whole length of the NOLM.
  • a NOLM comprising a fiber having a dispersion that is zero at the wavelength of the control pulse, either signal or clock, is discussed in U.S. Pat. No. 6,462,860.
  • this restriction on fiber dispersion may be hard to meet, since most commercial off-the-shelf fibers do not have this capability.
  • the control pulse would still suffer some shape degradation due to higher-order dispersion and self-phase modulation.
  • optical solitons preserve their temporal shape during propagation. Therefore, if a NOLM is controlled with a soliton control pulse, the output of the NOLM should comprise an optical pulse output that has a leading edge, a trailing edge and an intermediate plateau that provides for a true “top hat” shape. Hence, it is preferred that optical PPM receivers according to the present invention have top hat pulse generators that comprise NOLMs that are controlled by first order solitons. Further, using first order solitons, a fiber with positive dispersion (in ps/nm ⁇ km) supporting optical solitons should be used.
  • the soliton regime for the control pulse is achieved by (i) choosing a fiber with the correct, i.e., positive, dispersion sign and (ii) adjusting the peak power of the control pulse inside the loop to that of the first order soliton, as shown below:
  • a top hat generator 600 comprising a NOLM 610 controllable by a first order soliton is shown in FIG. 6 .
  • a coupler 620 preferably a 3 dB coupler, receives a continuous wave optical signal at optical wavelength ⁇ 1 at a first arm on a first side of the coupler 620 and launches two counter-propagating beams into a fiber loop 630 from the two arms on the second side of the coupler 620 .
  • the fiber loop 630 has positive (in ps/nm ⁇ km) dispersion.
  • a second arm on the first side of the coupler 620 produces the output signal from the NOLM 610 .
  • Another coupler 625 is used to launch a control pulse at optical wavelength ⁇ 2 in one direction into the NOLM.
  • a power control device 660 such as a fiber amplifier or attenuator, may be used to control the power of the control pulse.
  • the NOLM 610 may additionally comprise a polarization control device 680 .
  • an optical filter 670 (which may be a bandpass, stop band, or edge filter) at the output of the NOLM 610 is used to reject signals at the optical wavelength ⁇ 2 of the control pulse and to pass the resultant top hat pulse at the optical wavelength ⁇ 1 of the CW optical signal.
  • control pulse slides across the co-propagating counterclockwise CW signal due to dispersion and imprints a non-linear phase on the CW optical signal.
  • the interference of the clockwise and counterclockwise optical signals at the coupler 620 produces the top hat output.
  • the intensity of the top hat output is determined by the non-linear phase shift of the counterclockwise beam.
  • the components of the NOLM 610 discussed above are generally well-known in the art.
  • 3 dB couplers are available from any number of commercial vendors, and no specific 3 dB coupler is preferred for embodiments of the present invention.
  • the polarization control device 680 may be provided by devices and apparatus well-known in art and commercially available, such as a wave plate. Further, the polarization control device 680 may be located any where along the fiber 630 . Optical filters well known in the art may be used to provide the filter 670 .
  • the coupler 625 used to launch the control pulse into the loop may also be provided by a commercially available device.
  • the coupler 625 may comprise a 10 dB coupler, such that the CW optical signal propagating within the loop suffers 10% attenuation at the coupler, while the control pulse suffers 90% attenuation.
  • a 20 dB coupler may be used, such that the CW optical signal suffers only 1% attenuation, while the control pulse suffers 99% attenuation.
  • a 3 dB coupler which provides 50% attenuation of both the CW optical signal and the control pulse, may also be used.
  • a polarization coupler may be used to launch the control pulse into the loop at a polarization opposite that of the CW optical signal.
  • Equation (3) Typical parameters for a top hat generator that is controllable by a first order soliton are described as follows.
  • the peak power for achieving soliton regime is given by Equation (3) above.
  • the dispersion of a standard, that is, non dispersion-shifted, optical fiber is D ⁇ 17 ps/nm ⁇ km.
  • the dispersion of a positive dispersion-shifted fiber is typically D ⁇ 3-6 ps/nm ⁇ km, resulting in a peak power of P c ⁇ 10W.
  • These peak powers correspond to average powers of P avg ⁇ 400 mW and P avg ⁇ 100 mW, respectively, for control pulses with a 10 Gpulse/s repetition rate.
  • Control of the power of the control pulses may be provided by commercially available eridium-doped fiber amplifiers or attenuators, as discussed above.
  • the conversion efficiency for the NOLM controlled by solitons may be calculated as follows.
  • ⁇ NL max 4 ⁇ P c ⁇ ⁇ ⁇ ⁇ t 0 ⁇ 1 / v s - 1 / v c ⁇ Eq . ⁇ ( 4 )
  • ⁇ s and ⁇ c are the group velocities of the control pulse and continuous wave beams, respectively.
  • the denominator of Equation (4) can be calculated as follows:
  • 2 ⁇
  • ⁇ NL max 4 ⁇ P c ⁇ ⁇ ⁇ ⁇ t 0 ⁇ ⁇ 2 2 ⁇ ⁇ ⁇ ⁇ ⁇ 2 ⁇ ⁇ ⁇ Eq .
  • Equation (9) shows that the phase shift at the peak in a soliton-controlled NOLM depends only on the relative detuning of the control pulse from the CW beam.
  • the peak phase-shift depends upon the relative difference between the optical wavelength of the CW beam and the optical wavelength of the control pulse.
  • P TH peak P cw ⁇ sin 2 ⁇ ( ⁇ sol max ) Eq . ⁇ ( 10 )
  • P TH av P cw ⁇ sin 2 ⁇ ( ⁇ sol max ) ⁇ Dc Eq . ⁇ ( 11 )
  • Dc is the duty cycle of the top hat pulse, that is, the duration of the top hat pulse ⁇ t divided by the pulse-to-pulse period.
  • Dc is the duty cycle of the top hat pulse, that is, the duration of the top hat pulse ⁇ t divided by the pulse-to-pulse period.
  • Dc is the duty cycle of the top hat pulse, that is, the duration of the top hat pulse ⁇ t divided by the pulse-to-pulse period.
  • Dc should be less than or equal to 0.5.
  • an acceptable relative detuning value ⁇ / ⁇ FWHM should be found.
  • An acceptable relative detuning value is determined by the amount of control power leaking through the filter disposed at the output of the NOLM. In the calculations shown below, it is assumed that the control pulse has a sech 2 spectral shape and the filter has a top hat band shape.
  • FIG. 8 shows the relative cross-talk 810 , that is, the fraction of the control power leaking through the filter divided by the conversion efficiency, plotted versus the relative detuning.
  • the optimum detuning is determined from the system requirements for the maximum cross talk. If, for example, the relative cross talk should not exceed 10 4 ⁇ , the relative detuning should be approximately ⁇ / ⁇ FWHM ⁇ 3 (see FIG. 8 or Equation (15)), which gives a conversion efficiency P TH,out /P CW,in ⁇ 0.39 (see Equation (6) and FIG. 7 ). If higher cross-talk is tolerated, smaller detuning may be chosen, resulting in a higher conversion efficiency. For example, detuning of ⁇ / ⁇ FWHM ⁇ 2.27 may be desirable, which provides a maximum conversion efficiency of 45% and a cross-talk of 2 ⁇ 10 ⁇ 3 .
  • the output of the top hat generator will be independent of small variations in the control power, i.e., it will work as an optical limiter.
  • Equation (11) shows that the peak power of the top hat generator is dependent on sin 2 ( ⁇ sol max ). Therefore, if the generator is near the maximum efficiency, an increase or decrease in ⁇ sol max will only result in a slight decrease in output power.
  • the length of the fiber required for the NOLM is determined from the required pulse duration of the output top hat pulse. As described above, it is desirable to have a modulation index up to 0.5, therefore, top hat pulses having a relatively long duration are desired. However, the pulse repetition rate will limit the spacing and, therefore, the duration of the top hat pulses.
  • LD ⁇ Eq.

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PCT/US2003/015683 WO2003101014A1 (fr) 2002-05-23 2003-05-19 Generateur d'impulsion optique en omega
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US20050013543A1 (en) * 2003-07-18 2005-01-20 Hrl Laboratories, Llc. Method and apparatus for optical top-hat pulse generation
US20050095010A1 (en) * 2003-11-03 2005-05-05 Ionov Stanislav I. Method and apparatus for PPM demodulation using a semiconductor optical amplifier
US7515835B1 (en) 2004-10-25 2009-04-07 Hrl Laboratories, Llc System, method and apparatus for clockless PPM optical communication
US20110002348A1 (en) * 2009-07-06 2011-01-06 Institut National D'optique Adjustable pulsewidth picosecond fiber laser
US8569675B1 (en) 2011-03-10 2013-10-29 Hrl Laboratories, Llc Optical analog PPM demodulator

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KR100492979B1 (ko) * 2003-01-02 2005-06-07 삼성전자주식회사 대역 소거 필터를 적용한 ｅｍｌ 송신기
US8526829B1 (en) 2004-10-25 2013-09-03 Hrl Laboratories, Llc System, method and apparatus for clockless PPM optical communications
US7149029B1 (en) 2005-01-11 2006-12-12 Hrl Laboratories, Llc Interferometric PPM demodulators based on semiconductor optical amplifiers
CN103546218B (zh) * 2013-09-29 2016-04-13 华中科技大学 基于光学环镜的超宽带脉冲编码调制装置
CN109698458B (zh) * 2019-01-24 2020-02-07 广东朗研科技有限公司 非线性环路滤波的Mamyshev型激光振荡器

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US7605974B1 (en) 2003-11-03 2009-10-20 Hrl Laboratories, Llc Method and apparatus for PPM demodulation using a semiconductor optical amplifier
US7515835B1 (en) 2004-10-25 2009-04-07 Hrl Laboratories, Llc System, method and apparatus for clockless PPM optical communication
US20110002348A1 (en) * 2009-07-06 2011-01-06 Institut National D'optique Adjustable pulsewidth picosecond fiber laser
US8144737B2 (en) 2009-07-06 2012-03-27 Institut National D'optique Adjustable pulsewidth picosecond fiber laser
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WO2003101014A1 (fr) 2003-12-04

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